Tungsten has been widely used in multiple levels in logic and memory devices. Typically, CVD W processes provide conformal tungsten film growth on the substrate where nucleation has started. As the device scaling continues, there are new applications and integrations, such as cobalt capping for cobalt contacts, and copper capping for backend, that may use selective tungsten growth only on certain area of the pattern.
During the process flow integration, selective tungsten processes may lose selectivity due to the prior processing steps. For example, on a patterned surface after chemical-mechanical planarization (CMP), severe selectivity loss from >50:1 to <5:1 has been observed between metal and dielectric surface.
For some selective cobalt process, an in-situ passivation process using a surfactant has been developed to improve selectivity. The passivation layer formed only reacts on dielectric surfaces instead of copper surface, so cobalt can only grow on copper substrate instead of on the passivated dielectric, therefore selectivity is significantly improved. However, current surfactants will not only passivate the dielectric surface but also the cobalt surface. Therefore, tungsten cannot grow on the cobalt surface either, leaving no tungsten growth at all.
Therefore, there is a need in the art for methods of selectively depositing a film onto one surface selectively over a different surface.